I have a 1986 Fiero SE without a working drivetrain in my garage. I have two 2.8 liter V6 engines, in pieces, and a 3-speed automatic transmission of dubious utility.
And sitting right next to all that I have a perfectly usable 1995 Escort drivetrain. Complete, fully assembled, needing nothing but fresh oil.
The Escort drivetrain makes 88 horsepower and something like 105 foot-pounds of torque. The equivalent Fiero drivetrain--using the 2.5 liter "Iron Duke" engine and a 5-speed transmission--would make 95 horsepower and 115 foot-pounds. So it would not be a performance upgrade.
But the fuel economy...the Escort drivetrain netted 36 MPG in an Escort, which weighs about as much as a Fiero does.
Making engine mounts isn't a problem--buy some plate steel, figure out what shapes are needed, cut, tack in place with the MIG, and then have the local welding shop do the finish welding for me. It would take some doing but it wouldn't be difficult; just tedious in spots. (Such as cutting 1/4 inch plate steel with a sawzall or cutoff wheel. *sigh*)
The shift linkage would take some doing. The Fiero uses cables, and the Escort uses a shift rod, but I've already got an idea how to take care of that issue; building an adapter wouldn't be that hard. (Again, just tedious.)
I'd need to get a set of Escort axles, the computer, and wiring harness. I have no idea if I could make a hybrid axle by combining parts from the GM and Ford axles, or if I'd have to have custom axles made. Probably the latter, but custom axles would be stronger than factory parts anyway.
Wiring the computer would be entertaining. I could eliminate the Fiero computer entirely. I'd have to run the speedo off of the Escort transaxle's VSS, which means I'd have to condition the signal from said VSS to conform to what the speedo expects, but that's not a hard thing for me to do. (I'm a DeVry graduate!) (You can go ahead and insert retching noises here, but I really am capable of doing things like that. Really.) Changing resistors in the tach to get it to read correctly for a 4-cylinder isn't hard, either.
Have to check what fuel pressure the Escort engine expects. An adjustible fuel pressure regulator would take care of that, probably. (I doubt that a V6 fuel pump would have trouble keeping up with the demands of a 4-cylinder engine.)
From here it looks like the axles will be the most egregiously expensive parts, at least if I have to buy custom ones. I can get the rest of what I need from a boneyard, and there are literal millions of Escorts out there. (Finding one with an uncut engine bay wiring harness, however, may be a bit challenging.)
After that, then I need only make a pipe to patch the Escort exhaust header into the Fiero exhaust system--and that means making one pipe. One.
Having done all the hard parts, if I were to go get a 1997 2.0 liter Escort engine, I'd keep the fuel economy and end up with more Duke-like power and torque, too.
The Escort engine is, as I recall, basically a Mazda engine. So what interesting possibilities would that open up? I wonder....
(cross-posted on Pennock's Fiero Forum.)